Perinatal Exposure to Lead or Diethylhexyl Phthalate in Mice: Sex-Specific Effects on Cardiac DNA Methylation and Gene Expression across Time.

BACKGROUND

Global and site-specific changes in DNA methylation and gene expression are associated with cardiovascular development, aging, and disease, but how the transcriptome and epigenome of the heart change across the life course in males vs. females and how chemical exposures early in life influence this programming have not yet been investigated.

OBJECTIVES

We used an established mouse model of developmental exposures to investigate the effects of perinatal exposure to either lead (Pb) or diethylhexyl phthalate (DEHP), two ubiquitous environmental contaminants that are both strongly associated with cardiovascular diseases (CVDs), on DNA methylation and gene expression across the life course in whole hearts.

METHODS

Dams were randomly assigned to receive human physiologically relevant levels of Pb ( in water), DEHP ( chow), or control water and chow. Exposures started 2 weeks prior to mating and continued until weaning at postnatal day 21 (3 wk of age). Approximately 1 male and 1 female offspring per litter were followed to 3 wk, 5 months, or 10 months of age, at which time whole hearts were collected ( per sex per exposure). Enhanced reduced representation bisulfite sequencing (ERRBS) was used to assess the cardiac DNA methylome at 3 wk and 10 months, and RNA-Seq was conducted at all three time points. MethylSig and edgeR were used to identify age-related differentially methylated regions (DMRs) and differentially expressed genes (DEGs), respectively, within each sex and exposure group. Cell type deconvolution of bulk RNA-Seq data was conducted using the MuSiC algorithm and publicly available single-cell RNA-Seq data.

RESULTS

Thousands of DMRs and hundreds of DEGs were identified in control, DEHP, and Pb-exposed hearts across time between 3 wk and 10 months of age. A closer look at the genes and pathways showing differential DNA methylation revealed that the majority were unique to each sex and exposure group. Overall, pathways governing development and differentiation changed across time in all conditions. A small number of genes in each group showed significant differences in DNA methylation and gene expression with life stage, including several that were different in toxicant-exposed but not control mice. We also observed subtle but significant differences in the proportion of several cell types that were associated with life stage, sex, or developmental exposure.

DISCUSSION

Together these data suggest that gene expression and DNA methylation programs, as well as cellular composition, may differ across the life course long after cessation of exposure in perinatal Pb- or DEHP-exposed mice compared to controls and highlight potential biomarkers of developmental toxicant exposures; however, additional studies are required for confirmation. Further studies are also needed to investigate how epigenetic and transcriptional differences impact cardiovascular health across the life course, particularly in old age when the risk of cardiovascular diseases is markedly increased. https://doi.org/10.1289/EHP15503.